Global laptop shipments surpassed desktops in the third quarter, marking the first time mobile PCs have led the market, a research firm said Tuesday.

Laptop shipments rose by nearly 40% in the quarter compared with the same period last year to reach 38.6 million units, according to iSuppli. Desktop shipments, on the other hand, dropped by 1.3% to 38.5 million units.

The watershed event was expected, given that laptop shipments have been increasing by double digits for some time, while desktops have been in the low single digits.

"However, this marks a major event in the PC market because it marks the start of the age of the notebook," iSuppli analyst Matthew Wilkins said in a statement. "The notebook PC is no longer a tool only for the business market or a computer for the well-off consumer; it's now a computer for everyman."

While the scale of the global economic downturn became apparent in the third quarter, the impact had yet to be felt in the worldwide PC market, which saw an overall increase of 15.4% to 79 million units. ISuppli had predicted a 12% growth rate.

There was no change in the rankings of the top five PC makers in terms of shipments. Hewlett-Packard led the market with an 18.8% share, followed by Dell, 13.9%; Acer, 12.2%; Lenovo, 7.5%; and Toshiba, 4.6%.

Acer had an exceptional quarter. Shipments soared 79% year over year. The company shipped almost 3 million more laptops than in the second quarter, with most of those systems being netbooks.

The fast-growing netbook category is defined as ultralight, ultraportable PCs with screen sizes of 10 inches or less. Prices are often as low as $300.

Outside of the top five, No. 7 Apple lost nearly half a point of market share from the second quarter, falling to 3.2%, iSuppli said. Asustek surpassed Lenovo to become the fifth-largest laptop maker. Asustek was No. 6 in the overall market.

While PC shipments were strong in the third quarter, the global economic slowdown is expected to eventually take its toll. Research firm IDC reduced its shipment forecast for next year to 3.8% over this year, with global revenue falling by 5.3%.